I have a suggestion for the transmitters I had a similar problem when looking for a pre-made remote's for a Traffic light system I made for loading bays in work, I came across "AM Keeloq" Transmitter's and receivers.

The transmitters are 1-4 buttons, they are Encrypted (keloq) so they cant be copied easily but more importantly they have a unique serial number which the receiver can read via a serial output the transmitter is designed for 4 buttons it has momentary or latch operation, basically a garage door opener, however as I've said the transmitter's have a serial number so it should not be hard to associate a specific transmitter with a specific task in your program.

oh the receiver has built in memory and can store 50 unique remote's (although you wont need to memorise them as you will be using the serial output)

The encryption is totally automatic you don't need to do anything the only thing you will be interested in on the receiver is the serial output which gives the transmitters serial number and which button was pushed.

The reason I picked this set-up was because it was cheap £15 for the receiver and £14 for the 3 button remote, the remote's with less buttons were cheaper (£10 I think for a 1 button)

I had a quick look at the receiver's on the Linx website that was linked ..correct me if I'm wrong but if you use those receivers you set the channel by DIP switches or hard-wiring the channel in, so you would need a receiver for every remote ?